In general, a power distribution system is configured from a high-voltage system and a low-voltage system. A power receiving end of a general consumer is connected to the low-voltage system. A power company is obliged to maintain the voltage at the power receiving end of the general consumer in a proper voltage range. As an example, in the case of power reception of 100 volts, the power company is obliged to maintain the voltage at 95 volts to 107 volts. Therefore, the power company achieves the voltage maintenance at the power receiving end of the general consumer by adjusting a control amount of a voltage controller connected to the high-voltage system. Note that, in the following explanation, the power distribution system indicates the high-voltage system unless particularly noted otherwise.
A voltage controller of a transformer type such as an LRT (Load Ratio Transformer) or an SVR (Step Voltage Regulator) has an object of keeping the voltages at all points on a load side within a proper voltage range by changing the voltage on the load side according to tap operation based on LDC (Line Drop Compensator) control. In the LDC control, on the basis of an assumption that the voltage at a power distribution line end is lower as an electric current is larger, an appropriate load side voltage for keeping the voltages at all the points on the load side within the proper voltage range is calculated on the basis of voltage and current information measured by the voltage controller. The LDC control is based on the premise that a load distribution of a power distribution system is uniform, that is, the voltages at points in the power distribution system change in the same direction according to the elapse of time.
However, in recent years, because of the diversification of a way of using electricity and the spread of a distributed power supply, the load distribution of the power distribution system greatly changes according to the elapse of time. Therefore, a voltage situation of the entire power distribution system cannot be estimated only using the voltage and current information measured by the voltage controller. It is difficult to maintain the proper voltage. Therefore, for example, Patent Literature 1 described below discloses a system that a central voltage control device, which is a central device, collectively grasps measurement information of voltages and electric currents at points in the power distribution system via a communication network and commands a target voltage from the central voltage control device to the voltage controller.